The invention relates to a drilling tool comprising a drill head, a clamping shaft, and a helical shaft interposed between the drill head and clamping shaft.
Drilling tools composed of a plurality of individual parts are known. The multi-part nature of these relates not only to the insertion of carbide bits into the drill head, but to the multi-part design of the drill head and/or helical shank and/or clamping shank.
German Offenlegungsschrift 2,246,965 discloses, for example, a twist drill, in which the drill head and the helical shank are of two-part design, the drill head being attached positively onto the helical shank and being fixedly connected to the latter by a soldered joint. The purpose of such a multi-part joint is the employment of different materials for the two parts and, in particular, the use of a carbide drill head as a wear-resistant part. German Utility Model GM 83 28 156 has a similar design, and in this the drill head is subsequently connected to a drill rod and the parts are braced relative to one another via a transversely extending clamping sleeve. As a result, the drill head can be released from the drill rod in a simple way.
The two-part joint between the helical shank and the clamping end is likewise known. For example, German Offenlegungsschrift 2,811,977 discloses a carbide twist drill which is of two-part design in the region of the clamping shank, a press fit holding the parts firmly together.
A catalogue of Messrs Heller discloses, under the designation "Heller Ratio-Werkzeugsystem" ["Heller ratio tool system"], drilling tools for concrete and rock, the clamping ends of which have separate threaded extensions screwed into special drill receptacles or drill couplings which are themselves arranged fixedly in a machine tool. A drill change then takes place by the release of the threaded stem.
All the known solutions are based on the fundamental principle of connecting either the drill head or the clamping end to an, if appropriate, intermediate helical shank of a conveying helix, a fixed or releasable connection being used. A releasable connection can then be, for example, an additionally attached threaded device. The conveying helix itself is always selected irrespective of the connection of the individual parts which is to be selected.